Change of shaft diameter?

Discussion in 'Diesel Engines' started by Crocodile69, May 28, 2014.

  1. Crocodile69
    Joined: Feb 2014
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    Location: Key West

    Crocodile69 Junior Member

    Hey all,

    Hopefully someone out there can assist me on this one. Being built in South Africa, mostly everything on my boat is metric. And I am currently in the process of replacing my shaft, stuffing box, stern tube, split shaft coupler, etc..it's all been removed and I am now in the process with replacing everything new.

    I am replacing the 3 part bronze stern tube with a solid G10 epoxy tube. I am also looking to replace the stuffing box with a Norscot shaft seal.

    My only dilemna is the metric sizing of the shaft (approx 30mm in diameter or roughly 1-3/16"). Both G10 tubing and the shaft seal come only in standard sizing, not a big deal, as I can have a 'standard measurement' shaft installed. Though the shaft propeller seal kits are only available in 1-1/8" or 1-1/4", and my shaft lies almost in the middle of those measurements.

    I would like to keep the same diameter shaft that the vessel was designed for instead of going smaller or bigger.

    Any suggestions?
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Can you give an exact diameter size?
     
  3. Crocodile69
    Joined: Feb 2014
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    Crocodile69 Junior Member

    The majority of the shaft (between the coupler and the taper for the prop) is between 29.82 and 30 mm. Not sure if it's common for slight variations or if I need a new digital caliper. Where the shaft goes into the split coupler it goes down to 26.87. It's approximately 4' in length.
     
  4. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    3 mm is way more than a slight variation. It looks like it was reduced to fit a coupler. If you are using a stuffing box, the 1 1/4 will work fine. Teflon packing is the best material. It is softer, will seal better and stay cooler.
     
  5. Crocodile69
    Joined: Feb 2014
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    Crocodile69 Junior Member

    Thanks. Are there any issues with going larger from a shaft that was initially smaller in diameter? More work for engine? I have a Yanmar 3JH2E 34hp. Sorry to sound pretty naive in this field, first time I've had to pull a shaft and replace...
     
  6. gonzo
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    gonzo Senior Member

    Going from 1 3/16 to 1 1/4 is not a huge change. As long as the shaft tube is large enough it will not be a problem. However, make sure the propeller will fit properly in the taper. They may have to machine it slightly longer than usual. Measure the small diameter (aft side of the propeller) and the small diameter of the taper.
     

  7. Crocodile69
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    Crocodile69 Junior Member

    Thanks again gonzo.
     
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